Stroke is a common cause of death in the United States and disabling neurologic disorder. Approximately 700,000 patients suffer from stroke annually. Stroke is a syndrome characterized by the acute onset of a neurological deficit that persists for at least 24 hours, reflecting focal involvement of the central nervous system, and is the result of a disturbance of the cerebral circulation. Its incidence increases with age. Risk factors for stroke include systolic or diastolic hypertension, hypercholesterolemia, cigarette smoking, heavy alcohol consumption, and oral contraceptive use.
Hemorrhagic stroke accounts for 20% of the annual stroke population. Hemorrhagic stroke often occurs due to rupture of an aneurysm or arteriovenous malformation (AVM), causing bleeding into the brain tissue and resultant infarction of brain tissue. The remaining 80% of the stroke population are ischemic strokes and are caused by occluded vessels that deprive the brain of oxygen-carrying blood. Ischemic strokes are often caused by emboli or pieces of thrombotic tissue that have dislodged from other body sites or from the cerebral vessels themselves to occlude in the narrow cerebral arteries more distally. When a patient presents with neurological symptoms and signs, which resolve completely within 1 hour, the term transient ischemic attack (TIA) is used. Etiologically, TIA and ischemic stroke share the same pathophysiologic mechanisms and thus represent a continuum based on persistence of symptoms and extent of ischemic insult.
Emboli occasionally form around the valves of the heart or in the left atrial appendage during periods of irregular heart rhythm and then are dislodged and follow the blood flow into the distal regions of the body. Those emboli can pass to the brain and cause an embolic stroke. As will be discussed below, many such occlusions occur in the middle cerebral artery (MCA), although such is not the only site where emboli come to rest.
When a patient presents with neurological deficit, a diagnostic hypothesis for the cause of stroke can be generated based on the patient's history, a review of stroke risk factors, and a neurologic examination. If an ischemic event is suspected, a clinician can tentatively assess whether the patient has a cardiogenic source of emboli, large artery extracranial or intracranial disease, small artery intraparenchymal disease, or a hematologic or other systemic disorder. A head CT scan is often performed to determine whether the patient has suffered an ischemic or hemorrhagic insult. Blood would be present on the CT scan in subarachnoid hemorrhage, intraparenchymal hematoma, or intraventricular hemorrhage.
Traditionally, emergent management of acute ischemic stroke consisted mainly of general supportive care, e.g. hydration, monitoring neurological status, blood pressure control, and/or anti-platelet or anti-coagulation therapy. In 1996, the Food and Drug Administration approved the use of Genentech Inc.'s thrombolytic drug, tissue plasminogen activator (t-PA) or Activase®, for treating acute stroke. A randomized, double-blind trial, the National Institute of Neurological Disorders and t-PA Stroke Study, revealed a statistically significant improvement in stroke scale scores at 24 hours in the group of patients receiving intravenous t-PA within 3 hours of the onset of an ischemic stroke. Since the approval of t-PA, an emergency room physician could, for the first time, offer a stroke patient an effective treatment besides supportive care.
However, treatment with systemic t-PA is associated with increased risk of intracerebral hemorrhage and other hemorrhagic complications. Patients treated with t-PA were more likely to sustain a symptomatic intracerebral hemorrhage during the first 36 hours of treatment. The frequency of symptomatic hemorrhage increases when t-PA is administered beyond 3 hours from the onset of a stroke. Besides the time constraint in using t-PA in acute ischemic stroke, other contraindications include the following: if the patient has had a previous stroke or serious head trauma in the preceding 3 months, if the patient has a systolic blood pressure above 185 mmHg or diastolic blood pressure above 110 mmHg, if the patient requires aggressive treatment to reduce the blood pressure to the specified limits, if the patient is taking anticoagulants or has a propensity to hemorrhage, and/or if the patient has had a recent invasive surgical procedure. Therefore, only a small percentage of selected stroke patients are qualified to receive t-PA.
Obstructive emboli have also been mechanically removed from various sites in the vasculature for years. For example, the “Fogarty catheter” or variations thereof has been used, typically in the periphery, to remove clots from arteries found in legs and in arms. These well known devices are described, for example, in U.S. Pat. No. 3,435,826, to Fogarty and in U.S. Pat. Nos. 4,403,612 and 3,367,101. In general, these patents describe a balloon catheter in which a balloon material is longitudinally stretched when deflated.
In procedures for removing emboli using the Fogarty catheter or other similar catheters, it is typical, first, to locate the clot using fluoroscopy. The embolectomy catheter is then inserted and directed to the clot. The distal tip of the balloon catheter is then carefully moved through the center of the clot. Once the balloon has passed through the distal side of the clot, the balloon is inflated. The balloon catheter is then gradually proximally withdrawn. The balloon, in this way, acts to pull the clot proximally ahead of the balloon to a point where it can be retrieved. The majority of procedures using a Fogarty type catheter repeat these steps until the pertinent vessel is cleared of clot material.
A variety of alternative emboli retrieval catheters have also been developed, in which various wire corkscrews and baskets must be advanced distally through the embolic material in order to achieve capture and removal. However, removal of emboli using such catheters carries attendant potential problems. One such problem occurs when advancing the catheter through the clot dislodges material to a more remote site where removal may become more difficult or impossible.
Although neurointerventional devices and procedures have advanced, there remains a need for expeditious restoration of distal flow to blocked, or stenotic, cerebrovascular vessels, which can lead to severe neurological deficit or patient death.
New devices and methods are thus needed in treating vasculature occlusions in the body, including patients with acute ischemic stroke and occlusive cerebrovascular disease, in treating symptomatic patients with embolization or hemodynamic compromise, or in stroke prevention, e.g., patients with incidental finding of asymptomatic carotid lesion, which improve a patient's neurological function and quality of life without causing significant side effect, and can thus also be used in patients with contraindication to the use of t-PA.